Color-plus-clear coating systems that include a colored or pigmented base coat applied to a substrate followed by a transparent or clear topcoat applied on top of the base coat have long been the standard as original finishes for automobiles. The color-plus-clear systems have excellent aesthetic properties such as outstanding gloss and distinctness of image. The clear coat is particularly important for these properties.
Since the 1980's, damage to automotive coatings due to acid rain and other environmental acid has been a problem. Damage caused by acid exposure is particularly noticeable in automotive clear coats. Degradation of coating systems, which is caused by acid catalyzed hydrolysis of chemical bonds in the coating, can cause permanent surface blemishes, often appearing as groups of small pits resembling water spots or irregularly-shaped, rough-floored, low gloss depressions. Because of incident exposure to acidic environments such as acid rain, fog, and dew, it is essential that coating compositions used in automotive applications be resistant to degradation caused by acid exposure.
Prior art attempts to improve the acid etch resistance of coating compositions have included alternative chemistries that are less vulnerable to acid attack. Certain of these chemistries require expensive crosslinking agents or other components, and/or involve products of uncertain supply.
It would be desirable to provide new curable film-forming compositions yielding cured coatings that exhibit excellent acid etch resistance, while maintaining high gloss and other appearance and performance properties. Such compositions should use relatively inexpensive and easily prepared components, made from readily available ingredients and reactants.